[Gdal-dev] problem with resampling 16-bit data

[Michael P. Gerlek]

We've noticed a problem with reprojecting full 16-bit images when
using biliner or bicubic: the output image is speckled, presumably
due to over/underflow.  As verification, using the 20041210 snapshot
we recklessly replaced all occurrences of "GInt16" with "GUint16" in
gdalwarpkernel.cpp and the problem went away.

The command line to reproduce is just:
  gdalwarp.exe -t_srs EPSG:4326 -rb f.tif ff.tif
where f.tif is a simple 1-banded, 1Kx1K, unsigned, 16-bit geotiff --
whose dynamic range uses all 16 bits.

I've submitted this as #709 to Bugzilla, but the files won't seem to
attach -- they're small, I can mail them as needed.

-mpg

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Michael P. Gerlek
mpg at lizardtech.com
LizardTech, a Celartem company
Seattle, Washington
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